This invention relates generally to a binocular stereoscopic viewing device, and in particular, to a binocular ophthalmoscope for stereoscopic observation of the fundus of the eye by more than one observer.
During ophthalmoscopic examinations, the images representing the examiner's pupils and an observation light source are directed to the pupil of the eye to be examined. For optimum stereopsis, the images representing the examiner's pupils must be separated from each other as far as possible while falling within the pupil of the eye to be examined. The image representing the light source, which must also strike the pupil of the eye to be examined, should be separated as far as possible from the images representing the examiner's pupils.
Preferably, the images representing the light source and the examiner's pupils are separated as far as possible from each other within each eye to be examined by dilating each pupil to be examined through the application of a drug. Dilation of a patient's eye at times may not be possible or practical. To stereoscopically view the patient's pupil when dilation of the latter is not practical or possible, binocular ophthalmoscopy is employed.
One type of conventional binocular ophthalmoscope is disclosed in U.S. Pat. No. 4,684,227, the internal mirror array structure of an ophthalmoscope 100 being shown in FIG. 1. More particularly, this first type of conventional binocular ophthalmoscope includes a pair of internal mirrors 15 and a pair of external mirrors 16. Internal mirrors 15 and external mirrors 16 redirect and separate a pair of light rays 12 and 13 representing the stereoscopic image from a portion (e.g. fundus) of a patient's eye 11. Prior to reflection by internal mirrors 15, light rays and 13 pass through an ophthalmoscopic lens 14, for redirecting light rays 12 and 13. Internal mirrors 15 and external mirrors 16, in combination, guide light rays 12 and 13 to the observer's eyes (not shown) through a pair of oculars 17.
In the German Patent No. DE 3627251, another type of conventional binocular ophthalmoscope is employed. In this binocular ophthalmoscope, the optical observation paths from the patient's eyes are redirected several times by a relatively complex mirror configuration incorporated within the housing of the device. A reduction in the quality of the image to be examined results.
For clinical and tutorial applications, it is often necessary for more than one observer (e.g. instructor and student) to participate in the examination of the patient's eye at the same time. Conventional multi-user binocular or monocular ophthalmoscopes for multi-user application are disclosed in British Patent Specification No. 318,487 and publications by the firm of Zeiss, Oberkochen of West Germany entitled "Ophthalmoscopy Equipment" Prospectus No. W 30-131-d (1976) and "Stereo Assistant Tube" Prospectus No. W 30-047-d (1974). The multi-user ophthalmoscope disclosed in these references includes so-called assistant viewing tubes which are attached to the housing of a binocular or monocular ophthalmoscope 200 shown in FIG. 2.
More particularly, as shown in FIG. 2, Light rays 12 and 13 representing the stereoscopic image from a portion of eye 11 a patient are redirected by ophthalmoscopic lens 14 prior to striking an image splitter 28. Those portions of light rays 12 and 13 reflected by image splitter 28 are redirected to the assistant viewing tubes (not shown) along optical observation paths 20 and 21. Light rays 12 and 13 also pass through image splitter 28, are reflected by a pair of internal mirrors 25 and then by a pair of external mirrors 26 to redirect light rays 12 and 13 through oculars (not shown) prior to reception by an observer's eyes to form a stereoscopic binocular image. Each of the assistant viewing tubes receives a monocular ophthalmoscope image based on either optical observation path 20 or 21.
The multi-user ophthalmoscope 200 of FIG. 2 although providing for more than one observation at the same time is difficult to handle and susceptible to breakage, scratches, dust and dirt on various glass surfaces. Frequent replacement on the glass surfaces results. The intensity of light rays 12 and 13 diminished by the loss of light through image splitters 28 redirecting light toward the assistant viewing tube. Scattered light from one or more external sources through the assistant viewing tubes also interferes with the examination of the patient's eye.
Accordingly, it is desirable to provide an improved multi-user binocular ophthalmoscope which is easier to handle and less susceptible to breakage, scratches, dust and dirt on various glass surfaces. The ophthalmoscope also should prevent scattered light from external sources from entering into the device and thereby avoid scattered light from interfering with examination of the patient's eye.